The concept of high conductivity can be presented in two ways, and it can be shown that the properties thus highlighted are correlative:
In theory, it is shown that if an electrical field E is suddenly applied perpendicular to the free surface S of a conductive medium of permittivity .epsilon. and resistivity .rho., currents develop in this medium which bring, close to the surface S, electrical charges which resist the penetration of the external field within the medium, except into a surface layer whose thickness is very much less than a thousandth of a millimeter. This phenomenon however requires a certain amount of time and, during this time, the external field can penetrate the medium. This time is calculated by the formula .tau.=.epsilon..rho.. The liquid is of high conductivity if the time .tau. is very much less than the characteristic times of the electrical effects external to the medium, for example the period of the applied alternating electrical field.
In practice, a given volume (for example a 1 meter cube) of high conductivity liquid is traversed by high currents (for example hundreds or thousands of amperes) if a low voltage (of the order of a few volts) is applied between the faces of the cube; on the other hand, for a low conductivity liquid these figures can be respectively several nanoamperes for voltages of tens of kilovolts.
It follows that, in a high conductivity liquid, it is not possible to apply potential differences between two points in the liquid (or, which amounts to the same thing, to apply an electrical field of a measurable value to the liquid) without causing very high currents to pass through it, which is completely out of the question if, in the liquid, there are no conducting electrodes in direct contact with this liquid.
The invention relates in particular to the electrical treatment of mains or river water, used for example as cooling water, in order to avoid fur being deposited in the cooling equipment through which this water runs. It relates in particular to heat exchanger tubes and the cooling tubes in steam condensers, used in thermal or nuclear power stations. Another example relates to scrubbing water used to take away the excess aerosol paint produced during the painting of motor vehicle bodies using spray guns; this aerosol paint, in untreated water, forms a film which adheres to the walls, which poses difficult cleaning problems; if the water has been treated (for example electrically) the aerosol paint flocculates in the form of minute non-adherent elementary specks which are washed away by the stream of scrubbing water and which can easily be disposed of.
There already exist many processes for treating liquids using the effects of electrical or magnetic fields. These processes, which aim to give these liquids properties helpful in the use of certain techniques, are all characterised by the fact that these fields penetrate the liquids on which they have to act.
First of all, various patents can be cited relating to the treatment of hydrocarbons serving as fuels for internal combustion engines, that is to say liquids which, unlike water, behave essentially as dielectrics.
For example, the U.S. Pat. No. 3,116,726 in the name of M J KWARTZ describes a device designed to improve combustion in internal combustion engines, this device being formed by a coil designed to subject the fuel to a strong magnetic field. The U.S. Pat. No. 4,373,494 in the name of MACMAHON also concerns the treatment of hydrocarbon fuels and describes a device making it possible to apply a strong electrical field to the fuel before its combustion. As the fuel is an insulating dielectric, the electrical field can penetrate it without difficulty. The MACMAHON patent is concerned with increasing the strength of the field within the fuel. The British patent 806 230, in the name of MELI, relates to a device designed to subject the fuel to electromagnetic fields. This does specify that it relates to a fuel and that the means intended to apply the fields are connected intermittently to the current source, which excludes any action involving the continuous application of a current or voltage. This feature is in fact essential since experts know that electromagnetic effects can be produced only by variable voltages or currents.
In addition, other patents are known relating to the application of electrical or magnetic fields to a liquid.
For example, the French patent No 70.31089, published under the number 2 059 215, in the name of the LABOR MUSZERIPARI MUVEK Company, relates to a process for treating liquids, in general, in which such liquids are made to move in a configuration of electrical fields formed by alternating fields, or are treated at rest by voltage pulses, the orientations of which form angles governed by a specific relationship involving the permittivities of the walls of the receptacle and of the liquid, it being possible to apply an additional magnetic or electrical field along the flow of the liquids. This patent is thus based on the existence of variations in the direction of application of the effect of the fields under consideration on the same fluid molecule, where such variations may result either from the change in orientation of the effect over time if the molecule is at rest, or from the change caused, because of the flow, by the passage of the molecule in fields of different directions.
The U.S. Pat. No. 4,073,712, in the name of MEANS et al, claims electrostatic treatment of water based on the penetration of the electrical field into the water. The patent describes a device of electrodes of which at least one is insulated and between which the fluid to be treated must pass. The patent specifies clearly that the percentage of the potential appearing within the liquid must exceed 50% of the total potential applied to the electrodes. These potentials are calculated using conventional capacitance formulae involving the permittivity of the liquid, the equivalent diagram of the assembly being formed by capacitors in series, which shows that the process involves the electrical fields entering fully into the liquid to be treated.
This process can therefore be applied only to liquids with extremely high resistance, for example oil, but certainly not to water, contrary to what is indicated in the patent.
On the other hand the invention applies, as already indicated above, to the treatment of liquids whose conductivity is sufficiently high to prevent the continuous electrical field from penetrating, in the absence of any passage of current, beyond a surface layer of a depth less than one thousandth of a millimeter. In the case of mains or river water, the permittivity has a constant value (M.K.S. units): EQU .epsilon.=8.854.times.10.sup.-12 .times.80=7.times.10.sup.-10 Fm-1
The resistivity depends on the purity of the water; it varies from 1 .OMEGA.m for water with a very high content of dissolved salts to 500 .OMEGA.m for very pure water. If the latter case (low conductivity water) is chosen by way of example: EQU .rho.=500 .OMEGA.m therefore .epsilon..rho.=3.5.times.10.sup.-7 S
The time during which the external field can penetrate within the liquid, consequent upon a sudden application by means for example of an electrode coated with insulation, is less than one millionth of a second. Thus not only a continuous electrical field but also alternating fields of industrial frequency up to megahertz levels are incapable of penetrating the water (on the other hand, as is well known, electrical fields at a frequency of 2.45 gigahertz in microwave ovens penetrate it easily).